Size-change and deposition of conventional and composite cigarette smoke particles during inhalation in a subject-specific airway model

• Published in: Journal of aerosol science Vol. 46; pp. 34 - 52
• Main Authors: Zhang, Zhe, Kleinstreuer, Clement, Hyun, Sinjae
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.04.2012; Elsevier
• Subjects: Aerosols; Chemistry; Cigarette smoke particles; Colloidal state and disperse state; Computational analysis; Exact sciences and technology; General and physical chemistry; Potential reduced exposure tobacco products; Respiratory deposition; Subject-specific human upper airways; Cigarette smoke particles; Computational analysis; Potential reduced exposure tobacco products; Respiratory deposition; Subject-specific human upper airways; Clouds; Growth; Lung; Coagulation; Risk; Potential; Modeling; Composite material; Mechanism; products; Cigarette; Particle; Dynamics; Diffusion; Deposition; Human; Motion; Composition; Computer simulation; Health; Potential reduced exposure tobacco; Exposure; Droplet; In vitro; Sedimentation; Inhalation; In vivo; Generation; Tobacco; Aerosols; Models
• ISSN: 0021-8502; 1879-1964
• DOI: 10.1016/j.jaerosci.2011.12.002

In light of the established health risks of cigarette smoking, less harmful cigarettes (or potential reduced exposure products (PREPs)) have been marketed. Thus, it is of interest to analyze and compare the inhaled droplet dynamics of conventional and new composite cigarette smoke particles (CSPs). Inhalation pattern, hygroscopic growth and deposition of different composite cigarette smoke particles (CSPs) have been simulated numerically in a subject-specific human respiratory airway model from the mouth to generation G9. The validated computer model has been developed to consider the interaction of different deposition mechanisms, including impaction, sedimentation, diffusion, hygroscopic growth, coagulation, as well as possible cloud motion under different exposure and steady breathing conditions (e.g., puffing, post-puffing and two-step inhalation). The computer simulation results are consistent with numerous in-vivo and in-vitro studies as well as whole-lung modeling for deposition of conventional CSPs including hygroscopic growth and cloud motion. It is demonstrated that changes in cigarette composition significantly influence the hygroscopic growth of CSPs. In general, the growth rate of new composite CSPs is larger than the conventional one if the initial water mole-fraction is lower in the droplet. Hygroscopic growth of the new composite CSPs is not a significant mechanism leading to elevated deposition in the oral and tracheobronchial (TB) airways, provided that the relative humidity in the lungs does not exceed 99.5% and the droplet size does not exceed 3μm; however, enhanced deposition may occur if the particles can grow over 3μm. In this case, the deposition patterns of CSPs may be controlled by changing the primary composition, especially the initial ratio of water and glycerol. The simulation data with cloud diameters of 0.15–0.2cm in the oral cavity and 0.5–0.6cm in the trachea closely match the in-vivo lung deposition measurements of highly dense (conventional) CSPs. Specifically, preferred deposition occurs in the upper airway region, i.e., from the oral cavity to the second bifurcation, with deposition fractions of about 13–22% from the oral cavity to the larynx and 40–57% in the TB airways. This study is helpful for quantitatively evaluating the dose-exposure and subsequent health effects of both conventional and potentially less-harmful cigarettes. ► Hygroscopic growth and deposition of different composite cigarette smoke particles (CSPs) in human airways were simulated. ► Changes in cigarette composition significantly influence the hygroscopic growth of CSPs, but hardly affect the deposition. ► Effect of cloud motions on deposition of CSPs was also simulated.